This application claims priority of European Patent Application No. 98309207.3, which was filed on Nov. 10, 1998.
This invention relates to methods of and apparatus for testing the mutual insulation between a plurality of conductors.
It is frequently necessary to test whether all of the conductors in a cable, or, more generally, in a plurality of conductors, are properly insulated from each other. It is a simple matter, when there are only a few conductors, to do this by carrying out current leakage tests on every pair of conductors, but, since the number of pairs of conductors rises as N(Nxe2x88x921)/2, where N is the number of conductors, the number of current leakage tests rises rapidly with the number of conductors.
It is the object of the present invention to provide a faster way of testing mutual insulation in such circumstances, and apparatus for carrying out such a method.
The invention is as set out in the independent claims. Particular forms of the invention are set out in the dependent claims.
I have found that if the number of conductors N lies in the range 2nxe2x88x921  less than N less than =2n only n current leakage tests are necessary. In each of the n tests the conductors are connected in two sets and the test is for current leakage between the sets. Thus, for each pair of conductors, if the conductors forming the pair are so arranged that they are in different sets of tests for at least one test, then the insulation (or current leakage) characteristics between the pair of conductors can be tested. This is true for any given pair of conductors. If, for example, there are 16 conductors and 4 tests, each pair of conductors, for example the first and third, must be in different sets in at least one of the four tests, so that at least one test will detect current leakage between that pair of conductors.
The advantage given by the invention becomes greater as n increases. Thus, some advantage is obtained with n=2, but more for n=3, more still for n=4 and increasingly more for n equal to 5, 6, 7 and 8 etc. Also, the maximum advantage for a given n is obtained when N=2n.